The present invention refers to a method and an apparatus for simultaneously producing oxygen and nitrogen from air fractionation by means of a single rectifying column.
It is known that air fractionation for firstly producing oxygen and nitrogen, and possibly argon and other rare gases, is obtained by subjecting liquid air to a distillation step and, due to the fact that boiling temperatures of the three main components are respectively rising for nitrogen, argon and oxygen, in any process nitrogen will be obtained on top of the distillation column, oxygen at the bottom thereof, whereas argon will accumulate in an intermediate position.
It is also known that all methods and apparatus now employed for simultaneously obtaining oxygen and nitrogen pure enough for industrial uses, all of them substantially deriving from the two fundamental process of Linde and Claude, are of the double rectification type, i.e. with two superimposed columns mutually separated by a heat exchanger, the lower one, also named exhaustion column, working at a pressure greater than the one existing in the upper or real rectification column, in which the reflux of liquid nitrogen takes place.
Obviously the use of a single distillation column, namely a process by single rectification, would be highly advantageous as regards the simplicity of building, the overall dimensions and installation costs.
Nevertheless the use of a single rectification tower such as the one of the original Linde cycle has given poor results, mainly when both O.sub.2 and N.sub.2 are desired to be got in the pure state as an outcome of the process. In fact, whereas the oxygen obtainable from the bottom of the column can have a satisfactory purity, the nitrogen leaving the top end of the same column yet contains generally at least 6% oxygen. Likewise it is possible to get N.sub.2 pure enough, whereas oxygen contains at east 5% N.sub.2 and Ar.